package com.cjl.demo.juc;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicReference;

/**
 * <p>Copyright: All Rights Reserved</p>
 * <p>Description:
 * 题目：实现一个自旋锁
 * 自旋锁好处：循环比较获取直到成功为止，没有类似wait的阻塞。
 * 通过CAS操作完成自旋锁，A线程先进来调用myLock方法自己持有锁5秒钟，B随后进行发现
 * 当前有线程持有锁，不是null,所以只能通过自旋等待，直到A释放锁后B随后捡到。
 *
 * </p>
 *
 * @ uthor chenjinliang
 * @ date: 2020/2/16
 */
public class SpinLockDemo {
    //原子引用线程
    AtomicReference<Thread> atomicReference = new AtomicReference<>();

    public void myLock() {
        Thread thread = Thread.currentThread();
        System.out.println(Thread.currentThread().getName() + "\t come in");
        while (!atomicReference.compareAndSet(null, thread)) {
        }
    }

    public void myUnlock() {
        Thread thread = Thread.currentThread();
        atomicReference.compareAndSet(thread, null);
        System.out.println(Thread.currentThread().getName() + "\t invoked myUnlock");

    }

    public static void main(String[] args) {
        SpinLockDemo spinLockDemo = new SpinLockDemo();
        new Thread(() -> {
            spinLockDemo.myLock();
            try {
                TimeUnit.SECONDS.sleep(5);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            spinLockDemo.myUnlock();
        }, "AA").start();

        try {
            TimeUnit.SECONDS.sleep(1);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        new Thread(() -> {
            spinLockDemo.myLock();
            try {
                TimeUnit.SECONDS.sleep(1);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            spinLockDemo.myUnlock();
        }, "BB").start();
    }
}
